June 7, 2013

Coral Recovery In Light Of Cyclone Yasi Shows Promise

The coral reefs on Australia´s Great Barrier Reef were devastated by Cyclone Yasi — a Category 5 Hurricane which made landfall in Queensland, Australia, on February 3, 2011.

A new study from the ARC Center of Excellence for Coral Reef Studies (CoECRS) shows that large numbers of coral larvae replenished the reefs within nine months of the cyclone. The findings, published in PLoS ONE, provide fresh hope for the ability of the world´s coral reefs to recover from destructive storms.

Cyclone Yasi all but obliterated the corals on exposed reefs when its 32-foot waves and 177 mph winds hit Queensland´s Palm Islands, according to Dr Vimoksalehi Lukoschek of CoECRS and James Cook University.

Lukoschek and colleagues have dived on the devastated region over the last two years, studying the extent of the damage and the potential for recovery.

“Before the storm exposed reefs were covered in hard corals like the branching Acropora, arguably the most important group of reef-building corals on the Great Barrier Reef,” Lukoschek says. “The destructive effects of the cyclone reduced overall coral cover on exposed reefs to less than 2 percent and Acropora accounted for less than 1 percent of coral cover.”

“Basically, cyclone Yasi removed all adult colonies of Acropora and only a few very small juveniles survived the cyclone. What we witnessed was absolute devastation, previously healthy reefs almost completely devoid of any live coral,” adds Lukoschek.

The reefs of the Palm Islands were largely sheltered and escaped the majority of the storm´s damage. Coral cover was around 25 percent after the storm, which was similar to the coverage before. The sheltered reefs, most importantly, had large numbers of adult colonies of Acropora following the storm. These colonies can produce larvae to replenish devastated reefs.

The scientists found that areas devastated by Cyclone Yasi had been partly overgrown with algae a year after the storm. However, areas that had escaped undamaged remained algae free and coral-dominated.

Most importantly, the study found that there was a high coral larval recruitment on exposed reefs that had been damaged by the storm following the first mass-spawning event after it. According to Lukoschek, this is good news because "it essentially means that reefs that were completely devoid of reproductively mature adult corals, which are needed to produce larvae, were being replenished by coral larvae from reefs that had not been impacted by the cyclone.”

The team is conducting ongoing genetic research to determine which reefs these coral larvae came from. "Nonetheless, regardless of where they came from, the rapid replenishment of devastated reefs by large numbers of new recruits, combined with the juvenile corals that survived the cyclone, suggests that the recovery process is underway."

“The take home message from our study for the GBR is that although cyclones can have a major destructive impact on coral cover, these impacts tend to be patchy and coral larvae coming in from less impacted sites has the potential to reseed impacted reefs leading to their recovery," says Lukoschek.

“Our research indicates that corals can recover if given a chance to do so. Nonetheless, if the recovery process is disrupted by cyclones occurring in quick succession, or by other disturbances, such as coral bleaching or starfish outbreaks, or hindered by chronic stressors, such as poor water quality, pollution or disease, then coral populations may fail to recover,” Lukoschek concludes.